Ovarian cysts during pregnancy
are mostly corpus luteum
cysts and sometimes hemorrhagic. So long as they are less than 15cm., they do not create much trouble. Most often they go unnoticed. If needed, they can be investigated after delivery. The sonogram report says that the fetus is well and the pregnancy is inside the uterus
. In case, as you suspect, the pregnancy could be twins and the ovarian cyst is due to ectopic gestation, there should have been pain and other symptoms of shock
as the ovarian pregnancy grows to some extent and later ruptures, but you did not have any. Please consult your doctor for further advice. Take care.